Barium (
IPA:
/ˈbɛːɹiəm/) is a
chemical element. It has the symbol
Ba, and
atomic number 56. Barium is a soft silvery
metallic alkaline earth metal. It is never found in nature in its pure form due to its
reactivity with
air. Its oxide is historically known as
baryta but it reacts with water and carbon dioxide and is not found as a mineral. The most common naturally occurring minerals are the very insoluble barium sulfate, BaSO
4 (
barite), and barium
carbonate, BaCO
3 (
witherite).